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ISSN 2522-1841 (Online) AZERBAIJAN CHEMICAL JOURNAL № 3 2022 ISSN 0005-2531 (Print)
UDC 547.52/68
METAL-POLYMER CATALYSTS IN THE REACTION OF BENZENE
HYDROGENATION
R.H.Suleymanova, N.A.Zeynalov, L.N.Qulubayova, A.R.Guliyeva, U.A.Mammadova,
E.H.Babayev
M.Nagiyev Institute of Catalysis and Inorganic Chemistry, NAS of Azerbaijan
suleyman.rena@gmail.com
Received 16.02.2022 Accepted 09.03.2022
Metal-polymer catalysts in the reaction of hydrogenation of benzene have been studied. Salts of nickel, palladium, and H2PtCl66H2O were used as metals, which were deposited on polymer carriers, in particular, on polyethylenepolyamine, poly-2-methyl-5-vinylpyridine, styrene copolymer with maleic anhydride, and poly-4-vinylpyridine. A number of polymer complexes were also synthesized, tuned to benzene hydrogenation products and cross-linked with N,N'-methylenebisacrylamide, a crosslinking agent. The temperature of the hydrogenation reaction was controlled within 20-600C. Hydrogenation was carried out in an autoclave. It has been established that complexes based on platinum and poly-4-vinylpyridine lead to a high yield of the product of incomplete hydrogenation of benzene, cyclohexene. Also, it has been established that the Pt-poly-2-methyl-5-vinylpyridine complex tuned to benzene and cyclohexene exhibits a higher catalytic activity.
Keywords: benzene, hydrogenation, metal-polymer complexes, polyvinylpyridines, crosslinking, tuning, cyclohexane.
doi.org/10.32737/0005-2531-2022-3-93-98 Introduction
By hydrogenation of benzene, cyclohexane is obtained, which is used for the production of adipic acid, caprolactam, and cyclohexanol. Some amount of cyclohexane is used as a solvent in the production of polyolefins and resins [1, 2].
Earlier, in the hydrogenation of aromatic hydrocarbons, metal catalysts were used: nickel, cobalt, copper, platinum, and palladium, obtained by reducing the corresponding oxides with hydrogen. At present, nickel, platinum, and palladium on various supports, such as activated carbon, alumina, silica gel, and polymeric sorbents, are the most well-known catalysts for the hydrogenation of aromatic hydrocarbons [3].
Hydrogenation reactions of aromatic hydrocarbons widely use catalysts with platinum group metals supported on various supports, which are currently widely used polymeric sorbents [4].
Catalysts with a polymer support, in which the metal is contained in the form of a complex, have been obtained to be efficient in the process of hydrogenation of benzene under mild conditions [5-7]. The creation of effective
metal complex catalysts based on polymer-containing complexes is the most promising, which allow not only to heterogenize the catalyst if necessary, but, acting as polydentate macroligands, also ensure its high stability.
Our aim is to create active and selective hydrogenation catalysts based on metal complexes with organic polymer complexing agents. Metal-polymer catalysts based on nickel, palladium and platinum, and such polymeric complexing agents as poly-4-vinylpyridine (P-4-VP), poly-2-methyl-5-vinylpyridine (P-2,5MVP), and copolymer styrene with maleic anhydride (CP-S+MA) and polyethylenepolyamine (PEPA) as well [8-11].
At present, much attention is paid to complexes in which polymer chain units containing various functional groups act as ligands. Polyvinylpyridines have in their composition a nitrogen atom in various positions relative to the main polymer chain. This affects their com-plexing ability, and consequently affects their catalytic activity. The aim of the given research is to obtain metal-polymer catalysts for the hydrogenation of benzene with the formation of
both complete and incomplete hydrogenation products - cyclohexadiene, cyclohexene and cyclohexane [12-15].
Experimental part and discussion of the results
Synthesis of the complex was carried out in a three-necked flask equipped with a stirrer, reflux condenser, and thermometer. The flask was placed in an electrically heated water bath, the temperature of which was adjusted within the range of 20-60°C using a contact thermometer. Polyethylenepolyamines, copolymers of maleic anhydride with styrene in a ratio of 1:1 and 4-vinylpyridine with styrene (3:1), as well as polyvinylpyridines based on 4- and (2-methyl-5)-vinylpyridines were used as polymeric ligands. The complexes were prepared using NiCh^O, PdCl2, and ^PtCh^O as metal salts. The polymer was dissolved in ethanol, after which, without stopping the displacement (at uninterruptedly mixing), an ethanol solution of the metal salt was gradually added. After the introduction of the salt solution, the complex formation continued for some more time. At the end of the complex formation, the reducing agent sodium borohydride (NaHB4) was introduced. The precipitate of the complex was placed on a Schott filter, sucked off with a water jet pump, and washed with ethanol. The complex was dried in a thermostat at 80°C.
To test the catalytic activity of the synthesized complexes, autoclaves for hydrogenation under hydrogen pressure (up to 10 atm) were used. The autoclaves were made of stainless steel (capacity 100 and 110 cm ) and
Table 1. Hydrogenation of benzene on various metal-polymer complexes
equipped with exemplary manometers for a pressure of 10 atm. On the lid of the autoclave, in addition to the pressure gauge, there is a valve for purging and filling with hydrogen. The bottom of the autoclave has a fitting for sampling, which was carried out after the system was properly bled.
According to the described methods, metal-polymer complexes were synthesized, the catalytic activity of which was tested in the reaction of liquid-phase hydrogenation of benzene.
Hydrogenation of benzene was carried out at temperature of 20-60°C, a hydrogen pressure of 0-10 atm, and catalyst concentration of 0.01-0.07 g/mL.
The results of experiments of benzene hydrogenation on various metal-polymer catalysts are presented in Table 1.
Where: V0 - volume of benzene into the autoclave, mL; g0 - mass of the metal-polymer complex, g/mL of benzene; T - reaction temperature, 0C; t - duration of the reaction, hour; P0 - initial pressure of hydrogen, atm; AP -pressure change over t time, atm.
As can be seen from the Table 1, Ni-polymer complexes based on PEPA and P-2,5MVP do not exhibit catalytic activity in the hydrogenation reaction under mild conditions (200C, 2 atm). Pd-polymer complexes based on CP-S+MA s and P-2,5MVP also show unsatisfactory results. The resulting Pt-polymer complexes based on P-4-VP made it possible to obtain cyclohexane, a product of complete hydrogenation, and cyclohexene, as an intermediate product.
№ Vq, go, T, t, Po, AP, Yield, %
mL g/mL 0C hour atm atm C6H12 Ofto
1 complex Ni - (PEP A)
5 0.0146 20 70 4.56 0 — -
2 complex Ni - P-2,5MVP
5 0.0400 20 27 2.00 0 — -
3 complex Pd - CP-S+MA
5 0.0120 60 5.5 6.1 0 - -
4 complex Pd - P-2.5MVP
5 0.0486 60-20 18 2.6 - - -
5 complex Pt-P-4-VP
5 0.066 60 40 7.83 1.60 7.6 2.2
6 5 0.040 60 5.5 6.80 - - 100
METAL-POLYMER CATALYSTS IN THE REACTION
To obtain complexes tuned to a hydrocarbon substrate, the procedure for their preparation was retained with the only difference that during the synthesis, the corresponding substrate was added to the ethanol solvent and there was no addition of sodium borohydride. In the latter case, the complex was treated directly into the hydrogenation solution before the experiment. Complexes for the hydrogenation of benzene were used both in uncrosslinked and crosslinked states [16, 17].
Crosslinking of the obtained complexes was carried out according to the following procedure: the complex dried in a thermostat was subjected to grinding in a vibrating mill for 1-2 minutes to a powder state. After adding a cross-linking agent (N,N'-methylenebisacrylamide) as 15-20% by weight of the complex, mixing continued in the mill until a homogeneous state. Tablets were prepared from the obtained mass by pressing under a pressure of 250 atm. The tablets were placed in an ampoule, the air was pumped out to a deep vacuum. The sealed ampoule was placed in a thermostat, where it was kept for 2-3 hours at 120-1300C. Before the
95
hydrogenation experiment, the tablets were again crushed in a mortar to a powder state. Table 2 shows the data characterizing the synthesis conditions for each sample.
As can be seen from the Table 2, the Pt-P-2,5MVP complex activated with NaHB4 has the highest activity. Tuned to hydrocarbon substrates cross-linked complexes are also active in the benzene hydrogenation reaction.
In connection with the positive results obtained on the above-mentioned complex, an attempt was made to increase its activity by conformational tuning to hydrocarbon substrates. The results of the given experiments are presented in Table 3.
Both uncrosslinked and crosslinked samples of the complexes were studied. The results of the experiments make it possible to judge the influence of the conformational tuning, cross-linking degree of macromolecules of the complex in the benzene hydrogenation reaction.
Table 4 shows the effect of conforma-tional tuning, crosslinking degree on the conversion of benzene to cyclohexane as well.
Table 2. Brief characteristics of metal-polymer complexes - hydrogenation catalysts
№ Complexes Units, Me mol /mol Tuning on substrate Activation of NaHB4 Cross-linking, % Hydrogenation
at synthesis before testing g0, g/mL Yield, %
C6H:0
Ni-polymer complex (untuned to the substrate)
1 Ni-P-2,5-MVP 2.8 - - - - 0.04 absent
2 2.3 - 1:1 - - 0.05
Pd-polymer complexes (untuned to the substrate)
3 Pd-P-2,5-MVP 4.2 - - - 15 0.01 absent
4 4.2 - - - - 0.05 0.28 -
5 Pd-CP-(S+MA) 5.0 - - - - 0.01 absent
6 Pd-P-4-VP 5.5 - 1:1 - - 0.02
Pt-polymer complexes (untuned to the substrate)
7 Pt -P-4-VP 7.2 - 4.1:1 - - 0.4 - 100
8 3.2 - 1:1 - - 0.066 7.60 2.20
9 Pt -P-2,5-MVP 2.0 - 1:1 - - 0.033 7-42 absent
10 5.1 - - - - 0.024 9.6-26
11 5.1 - - - 19.8 0.019 absent
Pt- polymer complexes (tuned to the substrate)
12 Pt -P-2,5-MVP 5.1 C6H6 - - 34.36 0.022 3.7 absent
13 4.9 C6H10 - - 33 0.021 7.2
14 5.2 C6H12 - - 30.32 0.024 5-9
15 5.1 C6H6 - - 26.35 0.021 5-30
16 4.9 C6H10 - - 24.25 0.027 5-7
17 5.2 - - 45 0.029 0.44 0.01
Table 4. Effect of conformational tuning, crosslinking degree on the conversion of benzene to cyclohexane. g0= g/mL, P = 8-9 atm, units /Pt-5:1.
Table 3. Hydrogénation of benzene on Pt-P-2,5-MVP complexes tuned to hydrocarbon substrates.
№ Vo, go, T, T, P0, AP, Yield, %
ml g/ml 0C hour atm. atm. C6H12 C6H12
Tuned to benzene (uncrosslinked)
1 5 0.022 20 3.75 8.12 0.40 2.4 OTC.
additive H2 - 60 3.20 8.80 0.20 3.7
Tuned to cyclohexene (non-crosslinked)
2 5 0.21 20 1.25 8.16 0.12 -
increasing T - 60 3.30 8.76 3.36 7.2
Tuned to cyclohexane (non-crosslinked)
3 5 0.024 60 3.50 9.2 1.88 4.9 OTC.
5 0.025 25 4.75 7.96 2.10 7.2
Tuned to benzene (crosslinked)
4 5 0.021 60 3.3 8.85 - 5.0 OTC.
5 0.020 24 4.0 8.24 0.52 2.0
Tuned to cyclohexene (crosslinked)
5 0.024 25 2,0 9.52 0.12 OTC. OTC.
5 increasing T - 60 3.7 9.92 0.68
5 0.036 60 5.25 9.80 0
3 0.027 60-20 22.3 8.40 2.08 7.0
Tuned to cyclohexane (crosslinked)
6 5 0.029 20 4.75 8.20 0
after 48 hours - 60 1.25 8.32 0.04 0.44 0.01
Experiment № Tuning substrate T, 0C t, hour %wt, C6H12 %wt / hour
Uncrosslinked samples of the complex
1 C6H6 60 3.25 3.70 1.1
2 C6H10 60 3.30 7.20 2.2
3 C6H12 60 3.50 4.9 1.4
4 20 4.74 7.20 1.5
Crosslinked samples (15-20%)
5 C6H6 60 3.3 5.0 1.5
6 C6H10 60-20 22.3 7.0 0.35
7 C6H12 60 1.25 0.44 0.35
Untuned, uncrosslinked sample
8 — 60 4.3 9.6 2.2
9 — 60-20 60 7.0 0.12
Among the crosslinked complexes, the sample tuned to benzene showed the highest activity. However, in comparison with the untuned one, its activity is lower, which is explained by the fact that in the crosslinked state, some of the active centers remain inaccessible to the reactants. Among the uncrosslinked ones, the cyclohexene-tuned catalyst sample has the highest activity. However, its activity is similar to that of an untuned sample. This conclusion is natural since in the uncrosslinked state, the active centers of the complex remain in an insufficiently fixed position relative to the chain, which even in a solid complex has some mobility.
Conclusions
A number of polymer complexes based on polyvinylpyridines of various structures, copolymer with maleic anhydride and polyethylene-polyamine with metals of variable valence - Ni, Pt, Pd has been synthesized.
The study showed that platinum complexes, especially those based on P-4-VP, are active in the reaction of liquid-phase hydrogenation of benzene. A selective and high yield of the product of incomplete hydrogenation of benzene -cyclohexene was found.
The tuning of polymer complexes to initial and intermediate products of benzene hy-
METAL-POLYMER CATALYSTS IN THE REACTION
97
drogenation was also studied. It has been shown that the structure of the ligands of the polymer complex has a significant effect on the direction and selectivity of the reaction. It has been established that Pt-P-2,5MVP complex tuned to benzene and cyclohexene exhibits a higher catalytic activity. Pt-P-4-VP complex shows the greatest interest for the production of cyclohexene. At certain conditions for the complex preparation, a selective and high yield of the cyclohexene, product of incomplete hydrogenation of benzene, was found.
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BENZOLUN HÍDROGENLO§MO REAKSÍYASINDA METALPOLÍMER KATALÍZATORLARI
R.H.Süleymanova, N.A.Zeynalov, L.N.Qulubayova, A.R.Quliyeva, Ü.O.Mammadova, E.H.Babayev
Benzolun hidrogenlaçma reaksiyasinda metalpolimer katalizatorlari ôyranilmiçdir. Keçid metallarindan olan nikelin, palladiumun duzlari, hamçinin H2PtCV6H2O polimer sorbentlara oturdulmuçdur. Polimer daçiyici kimi polieti-lenpoliamin (PEPA), poli-2-metil-5-vinilpiridin, stirolun malein anhidridi ila sopolimeri, poli-4-vinilpiridin götürülüb. Bundan baçqa benzolun hidrogenlaçma reaksiyasinin mahsullarina kôklanmiç, tikici agent olan N,N-metilen-bisakrilamid ila tikilmiç bir sira polimer komplekslar sintez olunmuçdur. Hidrogenlaçma reaksiyasinin temperaturu 20-
60°C-da tanzimlanmiíjdir. ffidrogenla§ma prosesi avtoklavda aparilib. Müayyan edilmiíjdir ki, Pt-poli-4-vinilpiridin asasinda olan komplekslarin i§tirakinda benzolun natamam hidrogenlaíjma mahsulu olan tsikloheksenin Qiximinin artmasi müíjahida olunur. Hamginin benzol va tsikloheksena koklanmi§ Pt-2-metil-5-vinilpiridin asasinda alinan komplekslar yüksak katalitik aktivliya malikdir.
Agar sozlsr: benzol, hidrogenla§ma, metalpolimer komplekslar, polivinilpiridinlar, tikilma, koklanma, tsikloheksan
МЕТАЛЛОПОЛИМЕРНЫЕ КАТАЛИЗАТОРЫ В РЕАКЦИИ ГИДРИРОВАНИЯ БЕНЗОЛА
Р.Г.Сулейманова, Н.А.Зейналов, Л.Н.Кулибекова, А.Р.Кулиева, У.А.Мамедова, Э.Г.Бабаев
Изучены металлополимерные катализаторы в реакции гидрирования бензола. В качестве металлов были использованы соли никеля, палладия, а также H2PtCV6H2O, которые были нанесены на полимерные носители, в частности, на полиэтиленполиамин, поли-2-метил-5-винилпиридин, сополимер стирола с малеиновым ангидридом, поли-4-винилпиридином. Также был синтезирован ряд полимерных комплексов, настроенные на продукты гидрирования бензола и сшитые сшивающим агентом N,N -метиленбисакриламидом. Температуру реакции гидрирования регулировали в пределах 20-60°С. Гидрирование проводили в автоклаве. Установлено, что комплексы на основе платины и поли-4-винилпиридина приводят к высокому выходу продукта неполного гидрирования бензола - циклогексена. Также, установлено, что более высокую каталитическую активность проявляет комплекс Р^поли-2-метил-5-винилпиридин, настроенный на бензол и циклогексен.
Ключевые слова: бензол, гидрирование, металлополимерные комплексы, поливинилпиридины, сшивка, настройка, циклогексан.
